Permanent restructuring of keratin hair fiber is a two stage process. The first step involves cleavage of the keratin cystine disulfide bond, while the second step involves the reformation of these bonds in a new configuration. This methodology has been used for both perming (i.e., adding curl to straight hair) and relaxing (i.e., removing or modifying curled hair). In the former case, a reducing agent (mercaptan) is used to cleave the cystine disulfide bond while in the latter case a strong alkali or reducing agent (sodium hydroxide, guanidine carbonate or mercaptan) is used. Mercaptan reducing agents, such as salts, esters and amides of thioglycolic, thiolactic, cysteine, etc., are often used as well as other mercaptans, such as cysteamine, thioglycerine, etc., and their derivatives. The use of strong alkalies such as sodium and potassium hydroxide, as well as guanidine carbonate, cleave disulfide bonds by a different chemical mechanism than mercaptans and are used exclusively for removal/modification and not for formation of curls.
Permanent waving of human hair is achieved by placing stress on the hair fiber by winding the fiber on a mandrel. The diameter of the resulting curl will be directly proportional to the diameter of the mandrel employed. A waving lotion containing a water soluble mercaptan is applied to cleave the cystine bonds which will relieve some of the fiber's stress. After rinsing, an oxidant, such as hydrogen peroxide, sodium bromate, or sodium chlorite is then applied to reform the disulfide (i.e., cystine) bonds in the new curled configuration.
Relaxation or modification of curled hair can be achieved by winding tightly curled hair onto mandrels having large diameters and treating the hair with mercaptans as described above. Another methodology is to apply a mercaptan or a strong alkaline chemical (i.e., lye, guanidine carbonate), formulated into a viscous creme base, onto the hair. This viscous creme product is usually applied with a brush and then carefully spread using a comb. Continuous combing action places stress on the curled hair, and the viscous creme holds it in a relatively straight configuration as the cystine disulfide bonds are being chemically cleaved. When the desired "curl-less" configuration is achieved, the alkaline treated hair, which does not require oxidative neutralization, is rinsed with water and washed with an acidic shampoo while the mercaptan treated hair is neutralized with a semi-viscous creme oxidant, such as hydrogen peroxide, sodium bromate, etc. Continuous combing during the neutralization process is necessary so as to maintain the hair in a straight configuration during disulfide bond reformation. When neutralization is complete, in approximately five minutes, the hair is rinsed with water. Either treatment will modify/remove curl from hair fibers.
The prior art includes Kaitz U.S. Pat. No. 4,982,780, which requires eight steps including a heat treatment using a heat-generating composition; Wu et al. U.S. Pat. No. 5,294,230 which uses a waving lotion containing sulfite, bisulfite, or hydrosulfite, together with a water-soluble mercaptan; and Rose et al. U.S. Pat. No. 5,277,206 in which diammonium dithiodiglycolate is applied as a separate "pre-fixation" step before peroxide neutralization.